1. Field of the Invention
The present invention relates to a method of producing connection electrodes for semiconductor integrated circuits, printed circuit substrates, glass substrates, flexible substrates, ceramic substrates or the like.
2. Description of the Related Art
It is known that soldering is utilized in a method of electrically connecting the connection electrodes of such as a semiconductor chip to those of another circuit substrate. In the method utilizing soldering, a solder layer is formed on the electrodes of either of the substrates to be connected by plating, printing or other techniques. The solder layer is then heated to a high temperature of the order of 200.degree.-250.degree. C., and fused with the electrodes of the other substrate for connecting purposes. In this method, accordingly, it is necessary to employ a metal, such as Au, Cu or Ni, having an affinity for solder.
However, it has been pointed out that such a high-temperature process utilizing soldering thermally damages circuit substrates and, in addition, the use of a metal having an affinity for solder leads to an increase in cost.
The present applicant is aware of a method of electrically connecting the connection electrodes by using an anisotropic conductive sheet which includes conductive particles dispersed in an adhesive. This method can be used to solve the problems of thermal damage and cost increase.
The anisotropic conductive sheet has anisotropy which exhibits electrical conductivity with respect to the direction in which pressure is applied to the sheet and also exhibits no electrical conductivity with respect to other directions. Specifically, in this method, such an anisotropic conductive sheet is inserted between electrodes, terminals or other portions to be connected. Then the portion of the sheet interposed between, for example, the electrodes, is pressed and heated in the direction of the thickness of the sheet, thereby forming the electrical connection between the electrodes.
The anisotropic conductive sheet is particularly suitable for use in connecting the terminal electrodes of a liquid crystal display panel of the type which employs ITO (Indium Tin Oxide) as wiring material. This is because that high-temperature heat should not be applied to such liquid crystal display panel.
The anisotropic conductive sheet has conductive particles dispersed throughout the entire resin serving as an adhesive. Accordingly, if adjacent electrode terminals are spaced close to one another an electrical short may occur due to the conductive particles.